EPR investigation of the high-temperature dynamics of the impurity-doped Heisenberg linear chain TMMC:Cu

Abstract
Frequency-dependent EPR experiments from 1 to 18 GHz were performed on tetra-methyl-ammonium-manganese-chloride (TMMC) doped with 1%, 4%, 7% and 9% Cu2+ to study the influence of magnetic impurities on the high-temperature dynamics. The experimentally observed omega L-1/2 dependence of the magnetic resonance linewidth on the angular Larmor frequency omega L demonstrates directly that the long-wavelength dynamics in the doped samples is diffusive in this case as in the pure undoped system. From the experiment it is possible to extract the exchange interaction constant mod JMnCu/kB mod to be 1.7+or-0.4K. This value obtained is comparable with that found in low-temperature experiments. Observations of half-field transitions are reported in this impure 1d system.